In this R21 application we propose to assess cellular, molecular and immune correlates of efficacy and safety of nanoparticle formulations using a well characterized malaria vaccine candidate as a model immunogen. A vaccine based on Pfs25 protein targeting the sexual stages of the parasite provides a direct approach to reduce malaria transmission. In Plasmodium falciparum, Pfs230 and Pfs48/45 proteins produced within the intra-erythrocytic gametocyte stages and Pfs25, expressed during the mosquito stage development of zygote into ookinete, represent well established target antigens of transmission-blocking antibodies. Antibodies recognizing specific conformational epitopes in these proteins are potent blockers of infectivity of malaria parasites in the mosquito. We have recently succeeded in recombinant expression and purification of re-folded Pfs25, for the first time in near native conformation, in E. coli. The purified protein (rPfs25) in experimental adjuvants elicited strong immunogenicity in mice. Better and safer adjuvants and delivery methods need to be developed for eventual human applicability. Nanoparticles are fast gaining acceptability as safe and effective vaccine adjuvants. We propose to develop Pfs25 - nanoparticle formulations (Aim 1) and evaluate functional immune response in inbred and outbred mice (Aim 3). We also propose to study the immune response-related host gene expression changes at the site of vaccine injection to gain mechanistic insights of Pfs25-nanoparticle vaccine efficacy (Aim 2). Finally studies are also proposed to investigate relevant vaccine safety parameters (Aim 4). These studies will provide better understanding of cellular and molecular correlates of immunogenic efficacy and safety of nanoparticle formulations, and also provide the basis for more in depth studies on vaccine development, in general.